The present invention relates to an air-fuel ratio detection system, or more in particular to a detection system for detecting the air-fuel ratio of the exhaust gas of an engine.
Conventional engine air-fuel detection systems for detecting the stoichiometric air-fuel ratio are widely used to control internal combustion engines.
In recent years, an air-fuel ratio detection system for lean burn control has been under development for improving the fuel economy. As an example, the U.S. Pat. No. 4,282,080 discloses a system widely known for detecting the lean-mixture air-fuel ratio from the critical current which flows when the oxygen diffused from a diffusion resistor is fetched by a solid electrolyte cell.
In another well-known system as disclosed in the U.S. Pat. No. 4,158,166 (JP-A-78-66292), on the other hand, the carbon monoxide or the like diffused from a diffusion resistor is reacted with the oxygen collected by a solid electrolyte cell, and the rich-mixture air-fuel ratio is detected by the critical current that flows in the solid electrolyte in this process.
Nevertheless, there are no conventional systems which are capable of detecting the air-fuel ratio over a wide range from lean to rich mixtures.